Evaluating Proton Dose and Associated Range Uncertainty Using Daily Cone-Beam CT

Abstract

PurposeThis study aimed to quantitatively evaluate the range uncertainties that arise from daily cone-beam CT (CBCT) images for proton dose calculation compared to CT using a measurement-based technique.MethodsFor head and thorax phantoms, wedge-shaped intensity-modulated proton therapy (IMPT) treatment plans were created such that the gradient of the wedge intersected and was measured with a 2D ion chamber array. The measured 2D dose distributions were compared with 2D dose planes extracted from the dose distributions using the IMPT plan calculated on CT and CBCT. Treatment plans of a thymoma cancer patient treated with breath-hold (BH) IMPT were recalculated on 28 CBCTs and 9 CTs, and the resulting dose distributions were compared.ResultsThe range uncertainties for the head phantom were determined to be 1.2% with CBCT, compared to 0.5% for CT, whereas the range uncertainties for the thorax phantom were 2.1% with CBCT, compared to 0.8% for CT. The doses calculated on CBCT and CT were similar with similar anatomy changes. For the thymoma patient, the primary source of anatomy change was the BH uncertainty, which could be up to 8 mm in the superior–inferior (SI) direction.ConclusionWe developed a measurement-based range uncertainty evaluation method with high sensitivity and used it to validate the accuracy of CBCT-based range and dose calculation. Our study demonstrated that the CBCT-based dose calculation could be used for daily dose validation in selected proton patients.

Potential margin reduction in prostate cancer proton therapy with prompt gamma imaging for online treatment verification

“…Artificial intelligence approaches can be beneficial for detecting relevant deviations from complex input data [15] . When considering re-planning on cone-beam CT based data, larger range uncertainty margins would be needed [16] which subsequently increases the need for online treatment verification.…”

Effectiveness of CT‐image guidance in proton therapy for liver cancer and the importance of daily dose monitoring for tumors and organs at risk

“…Further research is needed to achieve Hounsfield units (HU) of the same quality as those of conventional CT scans in a variety of patient conditions, and a high quality of HU values is also needed for the proton dose calculation based on the water equivalent density converted from the HU. 16 Conventional CT scanning is currently more suitable for CT-image guidance with dose monitoring. Studies using CT-image guidance have been conducted mainly to evaluate the effectiveness and technological development of onlineadaptive irradiation, [17][18][19] which uses in-room CT images as the conventional scans to create irradiation plans immediately.…”

“…In recent years, radiotherapy vendors have begun offering proton therapy facilities equipped with CT image guidance capabilities, but most facilities use a CBCT system. Further research is needed to achieve Hounsfield units (HU) of the same quality as those of conventional CT scans in a variety of patient conditions, and a high quality of HU values is also needed for the proton dose calculation based on the water equivalent density converted from the HU 16 . Conventional CT scanning is currently more suitable for CT‐image guidance with dose monitoring.…”

Dose mimicking based strategies for online adaptive proton therapy of head and neck cancer

“…First, the CBCT image quality was out of the scope of the study since our main objective was the comparison between adaptive strategies all computed on the same corrCBCT. Nevertheless, it is an important field of research in OAPT since improved CBCT image quality would enable more accurate evaluation, optimization, and proton dose calculation (Park et al 2015, Thummerer et al 2020, Li et al 2022.…”